Showing papers by "Trevor D. Price published in 1997"

Likelihood of ancestor states in adaptive radiation.

Abstract: Theories of ecological diversification make predictions about the timing and ordering of character state changes through history. These theories are testable by "reconstructing" ancestor states using phylogenetic trees and measurements of contemporary species. Here we use maximum likelihood to estimate and evaluate the accuracy of ancestor reconstructions. We present likelihoods of discrete ancestor states and derive probability distributions for continuous ancestral traits. The methods are applied to several examples: diets of ancestral Darwin's finches; origin of inquilinism in gall wasps; microhabitat partitioning and body size evolution in scrubwrens; digestive enzyme evolution in artiodactyl mammals; origin of a sexually selected male trait, the sword, in platies and swordtails; and evolution of specialization in Anolis lizards. When changes between discrete character states are rare, the maximum-likelihood results are similar to parsimony estimates. In this case the accuracy of estimates is often high, with the exception of some nodes deep in the tree. If change is frequent then reconstructions are highly uncertain, especially of distant ancestors. Ancestor states for continuous traits are typically highly uncertain. We conclude that measures of uncertainty are useful and should always be provided, despite simplistic assumptions about the probabilistic models that underlie them. If uncertainty is too high, reconstruction should be abandoned in favor of approaches that fit different models of trait evolution to species data and phylogenetic trees, taking into account the range of ancestor states permitted by the data.

Correlated Evolution and Independent Contrasts

Abstract: The use of the independent contrast method in comparative tests is studied. It is assumed that: (i) the traits under investigation are subject to natural selection; (ii) closely related species are similar because they share many characteristics of their niche, inherited from a common ancestor; and (iii) the current adaptive significance of the traits is the focus of investigation. The main objection to the use of species values in this case is that third variables which are shared by closely related species confound the relationship between the focal traits. In this paper, I argue that third variables are largely not controlled by the contrast methods, which are designed to estimate correlated evolution. To the extent that third variables also show correlated evolution, the true relationship among the traits of interest will remain obscured. Although the independent contrast method does not resolve the influence of third traits it does, in principle, provide a greater resolution than the use of the species mean values. However, its validity depends on the applicability of an evolutionary model which has a substantial stochastic component. To illustrate the consequences of relaxing this assumption I consider an alternative model of an adaptive radiation, where species come to fill a fixed niche space. Under this model, the expected value for the contrast correlation differs from that for the species correlation. The two correlations differ because contrasts reflect the historical pattern of diversification among species, whereas the species values describe the present-day relationships among the species. If the latter is of interest, I suggest that assessing significance based on the species correlations can be justified, providing that attention is paid to the role of potentially confounding third traits. Often, differences between contrast and species correlations may be biologically informative, reflecting changes in correlations between traits as an adaptive radiation proceeds; contrasts may be particularly useful as a means of investigating past history, rather than current utility of traits.

Isolation and characterization of microsatellite loci in a Phylloscopus warbler

Abstract: ferences between closely related species (Taylor et al. 1994), subspecies (Paetkau & Strobeck 1994) and populations of the same species (Bowcock et al. 1994). Roy et al. (1994) presented a thorough analysis at all three levels for wolves and their close relatives. Gotelli et al. (1994) were able to reveal hybridization between the Ethiopian wolf and domestic dogs, and others have used microsatellite variation to suggest recent population bottlenecks (Paetkau & Strobeck 1994). As more accurate models to analyse population structure data of microsatellite loci become available (Slatkin 1995) it appears likely that the study of microsatellite variation will contribute significantly to the fields of population genetics and conservation. In this paper we present information on the isolation and characterization of microsatellite loci in the warbler Phylloscopus occipitalis. Our research aims at investigating genetic structuring along an altitudinal gradient in its Himalayan breeding quarters and how this is related to morphological differentiation. Genomic DNA isolated from blood of an adult female large crowned leaf warbler Phylloscopus occipitalis was digested with MboI and electrophoresed in a 1.5% agarose gel. DNA fragments in the size range of 300–600 bp were excised from the gel and isolated by electroelution. A size selected library was then constructed by ligating the DNA into the vector M13mp18 (opened with BamHI), followed by transfection into E. coli DH5αF’ by electroporation (E. coli Pulser, Bio-Rad). According to the ratio of blue and white colonies 80% of the vectors contained inserted DNA. A total of P 40 000 colonies were screened using the oligonucleotides CA15 and GA15 end-labelled with γ32P-ATP. Nine positive clones were detected and sequenced (Table 1). The sequence of POCC3 happened to be identical to clone POCC2 although they were found on different plates. Primers were designed to have a Tm of 60 nC. The primers were used on putatively unrelated individuals of 16 Phylloscopus occipitalis sampled at Manali, Himachal Pradesh, India. In addition, we checked a family (male, female and four chicks) to look for inheritance patterns. Initial PCR amplifications were performed under the following conditions: 30 s at 94nC, 30 s at 55 nC, 30 s at 72 nC (28 cycles). Before the cyclic reactions the samples were incubated at 94nC for 3 min, and after completion at 72 nC for 5 min. Reactions of 10 μL included 50 ng of total genomic DNA, 0.2 mM of each nucleotide, 1.5 mM MgCl2, 0.4 μM of reverse primer, 0.2 μM of unlabelled forward primer, 0.02 μM of γ32P-ATP labelled forward primer and 0.5 units of Taq DNA polymerase. The PCR products were resolved on a 8% denaturing polyacrylamide gel (long ranger, Bio-Rad). Gels were dried and exposed for 3–36 h. The primers first used to amplify locus POCC1 failed to amplify one of the paternal alleles (see Callen et al. 1993). This was indicated by two of the chicks in the family not inheriting the father’s allele and that several of the screened individuals appeared to be homozygotes for rare alleles. When one of the primers was redesigned a new allele appeared in the father and the two chicks. Primers for locus POCC4 failed to amplify readily scorable products, perhaps because of the long A-repeat adjacent to the CA-repeat (Table 1). For locus POCC9 we failed to amplify altogether. This clone was very difficult to sequence (with many stops on both sides of the repeat) and one can speculate that the PCR failed for the same reason that caused stops to occur in the sequencing reaction. In total, primers designed for five of the clones reliably amplified polymorphic loci (1, 2, 5, 6 and 8). We also screened primers isolated from other species: four from loggerhead shrikes Lanius ludovicianus (N. Mundy MS), two from the pied flycatcher Ficedula hypoleuca, two from the barn swallow Hirundo rustica (Ellegren 1992) and six from reed buntings Emberiza schoeniclus (Hanotte et al. 1994). Of these, one loggerhead shrike primer pair (LS2), one pied flycatcher primer pair (PTC3) and one reed bunting primer pair (Escμ4) amplified variable microsatellite loci. All of the eight primer pairs found to be useful in P. occipitalis also showed to be variable in P. reguloides and for at least five of the loci in the willow warbler P. trochilus (Table 2). This supports earlier observations that microsatellite primers often work across species PRIMER NOTE

Evolution of breeding distributions in the old world leaf warblers (genus phylloscopus).

Abstract: Among Palearctic warblers of the genus Phylloscopus those species that breed farther north occupy larger geographical ranges than those which breed farther south (Rapoport's rule). We suggest that much of this pattern is a consequence of the differential ability of species to occupy areas rendered inhospitable during the Pleistocene. In support of this suggestion, the midpoint of breeding range in a north-south direction has been an exceptionally labile trait through evolutionary time. Comparisons of ecological attributes of those species breeding in the Himalayas with close relatives in Siberia implies a role for habitat tracking in determining which species have been able to colonize northern areas; hypotheses based on climate and climatic variability have less support. In addition there is a likely role for geographic barriers and/or biotic interactions in preventing some taxa from spreading from small southern ranges.

The Adaptive Significance of Colour Patterns in the Old World Leaf Warblers, Genus Phylloscopus

Abstract: The great diversity of colour patterns in birds remains largely unexplained (Burtt 1986, Butcher and Rohwer 1989). Experimental and comparative studies have been used to identify some adaptive correlates, including intra-specific communication (Hill 1990, 1994, Slagsvold and Saetre 1991, Saetre and Slagsvold 1992, Marchetti 1993), camouflage (Gaston 1974, Burtt 1986), abrasion resistance (Burtt 1986), inter-specific signalling (Baker and Parker 1979, Gbtmark 1993, 1995, Saetre et al. 1993) and flushing out prey (Jablonski 1996). While we might expect plumage patterns to represent a compromise between all these and other selection pressures, two hypotheses have been recently proposed to explain the diversity of colour patterns within the genus Phylloscopus (Old World leaf warblers). Marchetti (1993) ascribes a role for intra-specific communication (i.e., signalling to potential mates or competitors) in the evolution of colour patterns, whereas Jablonski (1996) suggests that conspicuous coloration might be important for flushing prey. In this note we assess the role of prey-flushing in the Phylloscopus warblers using quantitative data on foraging and colour patterns. Jablonski (1996) proposed that wing, rump and tail patches could be important in prey-flushing in the Phylloscopus warblers. To support this idea he used qualitative reports on foraging behaviour culled from the literature, and a cross-species comparative study to demonstrate an association of conspicuousness with the use of the wings during foraging. However, Burtt (1986) in a comparative study of the New World warblers also found an association between plumage brightness and foraging movements, but interpreted it as being a consequence of intra-specific communication. For example, species which flycatch are prominently displaying their wings, and therefore the wings are suitable locations to place patterns used in intra-specific communication. From Jablonski's prey-flushing hypothesis we predict positive correlations between plumage brightness and only those flying movements that lead to chases after flushed prey, but from Burtt's intra-specific communication hypothesis we expect a positive correlation between plumage brightness and the number of all types of flying movements performed by the bird when feeding. There are therefore two purposes to this paper. First, we demonstrate a correlation between plumage brightness and foraging among the Phylloscopus warblers using more quantitative data than were used by Jablonski (1996). Second, we use our results to compare the predictions of the intra-specific communication and prey-flushing hypotheses. Phylloscopus species differ in the number of colour patches they have. In all species, colour patches occur as bright, unpigmented areas on the tips of certain feather tracts of the body. Some species are essentially unpatterned and have uniform dark upperparts except for an eye-stripe. Others have one or two patches on the wings, a crown stripe, a rump patch and/or white tail patches in nested combinations, so that, for example, every species with crown or rump patches always has a wing patch (see Marchetti 1993, Price and Pavelka 1996). We used three different measures of plumage brightness for a species: 1. the total number of colour patches, varying from 0-5 (Marchetti 1993). 2. the total brightness (% reflectance relative to a standard, as measured by reflectance spectroradiometry), of the colour patch at the tip of the feather taken from the tract of feathers which form the largest wing patch on those species which have a wing patch (Marchetti 1993). 3. the size of the unpigmented patch on this same feather (area without melanin; Price and Pavelka 1996). The three variables are correlated (Fig. 1, Table 1). Quantitative data on foraging are available for eight Phylloscopus species from Kashmir, India (Price 1991). Feeding methods were classified into four main types: standpick (a prey capture not involving flight), flypick (prey resting on a leaf or branch, observed while hopping, but taken in flight), flycatch (capture of prey, which was nearly always flushed), and hoverpick (prey